I assume that this is probably some kind of driver problem if your midi device isn’t showing up. If the device is not class compliant, you might be out of luck. Whereas this doesn’t seem to specifically be an Ardour problem, you might get better help asking at the forum linuxmusicians.com

You need to be specific about what audio/MIDI backend you are using with Ardour. If you’re not already doing so, you should start by using the “ALSA” backend, which automatically finds all MIDI devices by itself. If that doesn’t show your device, then the problem is along the lines of Michael’s comment. If it does, then you were probably using JACK and not understanding the complexity of setting up MIDI with JACK (which is described in the Ardour manual): http://manual.ardour.org/setting-up-your-system/setting-up-midi/